not nessacarily, if the neck splits the shoulder of the case will seal it off, on cases with taper the casehead will hold back the pressure. but better find out why they are splitting.
RR
Probably not but its never a good thing. Brass probably needs annealed and even new brass can be too brittle and split. I have a large lot of .357 max brass that I got new that is too brittle to use without annealing first thing. Remington actually sent me replacement brass free gratis and let me keep the original stuff.